n,k=map(int,input().split())

if k%2==1:
  if n%2==1:
    print(min(n,2*(k//2+1)))
  else:
    print(min(n//2,2*(k//2+1)))
else:
  if n%2==1:
    print(min(n,2*(k//2+1)-1))
  else:
    print(min(n//2,2*(k//2+1)-1))